The folic acid antimetabolites aminopterin and amethopterin (also known as 10-methylaminopterin or methotrexate) are antineoplastic agents. These compounds inhibit enzymatic conversions involving metabolic derivatives of folic acid. Amethopterin, for example, inhibits dihydrofolate reductase, an enzyme necessary for the regeneration of tetrahydrofolate from dihydrofolate which is formed during the conversion of 2-deoxyuridylate to thymidylate by the enzyme thymidylate synthetase.
Other derivatives of folic acid and aminopterin have been synthesized and tested as antimetabolites. Among these are compounds in which a methylene or methylidene group occupies a position in the molecule normally occupied by an imino or nitrilo group respectively. These derivatives have varying degrees of antimetabolic activity. 10-Deazaaminopterin is highly active (Sirotak et al., Cancer Treat. Rep. 1978, 62, 1047) and 5-deazaaminopterin has activity similar to that of amethopterin (Taylor et al., J. Org. Chem., 1983, 48, 4852). 8,10-Dideazaaminopterin is reported to be active (U.S. Pat. No. 4,460,591) and 5,8,10-trideazaaminopterin exhibits activity against mouse L1210 leukemia (Yan et al., J. Heterocycl. Chem., 1979, 16, 541). 10-Deazafolic acid, on the other hand, shows no significant activity (Struck et al., J. Med. Chem., 1971, 14, 693) and 5-deazafolic acid is only weakly cytotoxic. 8, 10-Dideazafolic acid is only marginally effective as a dihydrofolate reductase inhibitor (DeGraw et al., "Chemistry and Biology of Pteridines", Elsevier, 1979, 229) and 5,8, 10-trideazafolic acid also shows only marginal activity against mouse L1210 leukemia (Oatis et al., J Med. Chem., 1977, 20, 1393). 5,10-Dideazaaminopterin and 5,10-dideaza-5,6,7,8-tetrahydroaminopterin, and the corresponding 5,10-dideazafolic acid derivatives are reported by Taylor et al., J. Med. Chem., 28:7, 914 (1985).